With the growth of print-on-demand market in the recent years, the demands for speeding up for electrophotographic technique are ever more increasing. Therefore, a polyester having a low softening point is widely used in order to fix a toner at low temperatures. However, mere use of a polyester having a low softening point leads to some disadvantages such as lowered durability and fusion of a toner to a member of the machine.
In view of the above, for example, JP-A-2001-51448 discloses a technique of a toner for electrostatic image development, in which a polyester resin containing isophthalic acid and an isophthalic acid derivative in an amount of from 25 to 50% by mol is used, whereby the resulting toner has excellent low-temperature fixing properties, is free from the generation of fusion to a developing roller or a blade, toner dust, background fogging, and the like, during a long-term continuous copying, and can realize stable image properties.
In addition, in high-speed continuous printing, the stress against the toner is strong, so that an external additive is likely to be embedded. If the fluidity is lowered due to the embedment of the external additive, the toner is disadvantageous in developability or transferability, in other words, more disadvantageous in durability, which in turn would cause the lowering of the image quality. In view of the above, JP-A-2005-352081 discloses a technique of a toner for electrostatic image development containing a negatively chargeable charge control agent and a positively chargeable charge control agent, and large-particle size fine inorganic particles having a BET specific surface area of from 20 to 30 m2/g as an external additive, thereby suppressing the external additive from being embedded, so that excellent fluidity is maintained.